A group of transforming growth factors (TGF's) have been identified in both normal and transformed cells from a variety of tissue types. These factors, which are effectors of malignant phenotypic transformation, appear to be peptides possibly related to epidermal growth factor (EGF), and EGF markedly enhances the action of some TGF's. Thi study will attempt to define structure-function relationships of the EGF, and ultimately the TGF molecules, through synthetic and chemical modification techniques, primarily to gain information for the rational design of effective inhibitors. Seven C-terminal synthetic fragments of EGF have been prepared by solid phase methodology to date and are being examined in a variety of assays for receptor binding and biological activity (agonist and antagonist). In addition, several modifications to the native molecule have been made and, more are planned, to identify residues or regions of specific importance. Efforts to prepare larger synthetic fragments by solid-phase, as well as fragment condensation techniques, are under current investigation.